ARM: zynq: Convert dlc20 and zc70x board to DM_I2C

All these board have also eeprom enabled that's why it is also enabled
via defconfig.
There is also no need to have zc70x specific config file that's why also
remove it.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Heiko Schocher <hs@denx.de>